1. Field of the Invention
The present invention relates generally to a method and system for producing a flip chip type semiconductor device. More specifically, the invention relates to a method and system for attaching or loading conductive balls serving as connecting terminals onto a ball grid array (BGA) substrate or board or substrate attached with semiconductor elements or directly onto semiconductor elements.
2. Related Background Art
It is conventionally known that a flip chip type semiconductor device has high level function and high reliability in a high-speed, high-level-function package for use in the field of computers and communication equipment, or in a chip size package (CSP) for use in the field of portable equipment.
In particular, a flip chip BGA type semiconductor device is produced as follows. First, a chip-like semiconductor element is flip-chip-attached to a multilayer interconnection substrate (which will be hereinafter referred to as a "BGA substrate"), which uses an organic material, such as bismaleimide triazine (BT) resin or an epoxy resin, as an insulating plate, via connecting terminals of conductive balls of solder, gold or the like. Moreover, the connecting terminal of the conductive balls is mounted on the BGA substrate, and the BGA substrate is attached onto a mounting substrate via the connecting terminal. Alternatively, there is another semiconductor device wherein connecting terminals of conductive balls are mounted directly on a chip of semiconductor elements, which is flip-chip-attached to a mounting substrate.
In order to load the conductive balls onto the BGA substrate or semiconductor element, a conductive-ball attaching system is used.
Referring to FIGS. 15 through 19, a method for attaching conductive balls onto a BGA substrate or semiconductor element using a conventional conductive-ball attaching system will be described below.
FIG. 15 is a flow chart showing a conductive-ball attaching process using a conductive-ball attaching system. First, after a BGA substrate or semiconductor element is introduced into a conductive-ball attaching system (step 1), conductive balls are vacuum held by a jig called a attaching head having ball vacuum-holding holes in alignment with the electrodes of the BGA substrate (step 2). Then, it is examined by image recognition or the like whether the conductive balls vacuum-held by the attaching head are correctly aligned (step 3). Then, a flux is supplied to any one of the BGA substrate or semiconductor element and the conductive balls vacuum-held by the attaching head (step 4), and the conductive balls are attached onto the electrodes of the BGA substrate or semiconductor element (step 5). Thereafter, it is examined whether the conductive balls remain on the attaching head (step 6), and then, it is examined whether the conductive balls are correctly attached on the BGA substrate or semiconductor element (step 7). Thereafter, the conductive balls are molten and attached to the electrodes of the BGA substrate or semiconductor element by reflow to be fixed to the BGA substrate or semiconductor element (step 8).
FIG. 16 is a sectional view of a conventional ball attaching system. A attaching head 1 for vacuum holding a prescribed number of conductive balls 6 at prescribed positions to load the conductive balls onto a BGA substrate 9 or the like is secured to moving means 2, which is moved by a feed screw (XY) 10 in X and Y directions (horizontal directions), and to moving means 3, which is moved by a feed screw (Z) 11 in Z directions (vertical directions). When the attaching head 1 vacuum holds the conductive balls 6, the attaching head 1 moves above a ball storage vessel 4, in which the conductive balls 6 are stocked. When the vacuum-held conductive balls 6 are moved to the BGA substrate or the like, the attaching head 1 moves above a stage 5. The BGA substrate 9 is secured to the stage 5 by means of a substrate clamper 14.
The vacuum holding of the conductive balls 6 is carried out by evacuating the interior of the attaching head 1 via an air passage (suction side) 12 by air suction means 7 to allow the internal state of the attaching head 1 to be a reduced pressure state to suck the conductive balls 6. In addition, a flux is supplied to the electrodes of the BGA substrate 9 or the like, or to the vacuum-held conductive balls 6 by flux supply means (not shown).
Moreover, when the conductive balls 6 are attached onto the BGA substrate 9 or the like, air is fed into the attaching head 1 via an air passage (exhaust side) 13 by air flow generating means 8 to turn the reduced pressure state into an atmospheric pressure state to detach the conductive balls 6 from the attaching head 1.
FIG. 17 is a sectional view showing the attaching head and the storage vessel when the conductive balls are vacuum held. The internal state of the attaching head 1 is turned to the reduced pressure state by the air suction means 7, so that the conductive balls, which have been turned into flowable balls by means (not shown), are sucked into ball vacuum-holding hole 17 of the attaching head 1. At this time, air passage opening and closing means 15 provided in the air passage 12 extending from the air suction means 7 to the interior of the attaching head 1 is open, and air passage opening and closing means 16 provided in the air passage 13 extending from the air flow generating means 8 to the interior of the attaching head 1 is closed.
FIG. 18 is a sectional view showing the attaching head and the BGA substrate on the stage when the conductive balls are attached onto the electrodes of the BGA substrate or the like. When the conductive balls 6 are attached, the air passage opening and closing means 15 provided in the air passage 12 is closed, and the air passage opening and closing means 16 provided in the air passage 13 is open. Thus, air is fed into the attaching head 1 to turn the internal state of the attaching head 1 into the atmospheric pressure state to detach the conductive balls 6 surrounded by a flux 18 from the ball vacuum-holding holes 17 to load the conductive balls 6 onto the BGA substrate. This BGA substrate is secured to the stage 5 by means of the substrate clamper 14.
Such a conductive-ball attaching process is not carried out every BGA substrate in order to improve productivity. For example, as shown in FIG. 19, conductive balls 6 are usually collectively attached onto a plurality of BGA substrates 9 or semiconductor elements. FIG. 19 is a sectional view showing the attaching head 1 and the BGA substrate 9 on the stage 5 when the conductive balls 6 are attached onto the electrodes of the BGA substrates 9 or the like.
As the form of a substrate, there are an individual piece substrate comprising a set of a plurality of substrates (units) secured to a stage 5 by means of a substrate clamper 14, and a single strip substrate, on which a plurality of semiconductor elements (units) are attached. In either case, a attaching head 1 capable of vacuum holding conductive balls 6, the number of which corresponds to the number of the units, is used. As the substrate having the plurality of semiconductor elements (units), a wafer, from which semiconductor elements have not been cut in the form of chips, is used.
However, as shown in FIGS. 20(a) and 20(b), there are some cases where the strip substrate 19 has defective substrates shown by a defective mark 21. Even in such cases, the conductive balls must be attached onto the defective substrates in the present circumstances, so that the conductive balls are wasted to cause a rise in costs. FIGS. 20(a) and 20(b) are plan and sectional views showing a strip substrate attached with a plurality of semiconductor elements 22, each of which is coated with a sealing material 23 and each of which has a plurality of electrodes 20.
Moreover, in a case where the conductive balls 6 are attached onto a wafer 24 as shown in FIG. 21, if the semiconductor elements 22 are not arranged on the wafer 24 in the form of a square grid, undesired conductive balls 26 are attached on a peripheral portion other than the semiconductor elements. This has a bad influence on the system, and wastes the conductive balls 6. FIG. 21 is a perspective view of a part of the wafer 24 which is divided into the plurality of semiconductor elements 22 by dicing lines 25.